Sealed hinge lines? Are we absolutely sure about this???

[Claudio Chacon]

Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!

Many of you in this forum know very well Sergey, and you know that he ain't no rookie!

Please, check out the pics attached (and enlight me!)

Thanks!

[Joshua Harel]

Could it possibly be that the pilot's ability is far more important than the gap?

[Shultzie]

Unsealed hinges...seem to work wonders waaaay back in 1968 when "The Bear" won the nats with his GGopler' and ol' Fox 35 Hummm? But by today's standards but again------------we were then "judged by a different set of NAVY standards?"

[Tim Wescott]

From the explanations of why one seals hinge gaps, those gaps look to be engineered specifically to work without sealing.

Those gaps are large (which means that small changes in gap spacing won't make a big difference), and pivot is buried in the elevator, meaning that the elevator leading edge sticks up above the stab, which should cause some turbulation effect (I don't know if it'll work, but that looks to be the intent).

Fellows with a less casual acquaintance with aerodynamics than me may have something to add, but it looks like he's found a good alternative.

And who knows?  Maybe he would have taken first place if he'd used conventional hinges and sealed the gaps?

[FLOYD CARTER]

Often, aileron hinge points on full size aircraft are located ahead of the gap.  Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.

Floyd

[Dan McEntee]

  Might be the reason he finished 14th instead of higher?

   Full scale acro aircraft use sealed hinge lines. There is no reason that the model wouldn't fly and do the pattern, and there might be some quirky exception to the laws of physics for this, but I kinda doubt it.
    Dan McEntee

[EddyR]

What is the best clear tape to use to seal hinges? I can't get any to stick to my Bearcat
Ed

[don Burke]

Often, aileron hinge points on full size aircraft are located ahead of the gap.  Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.

Floyd

A minor point, that works if the hinge axis is BEHIND the LE

[Dennis Moritz]

I notice there are flies. It's the inexplicable boost from the flies.

[Tim Wescott]

What is the best clear tape to use to seal hinges? I can't get any to stick to my Bearcat
Ed

What's on my bench is Scotch "Gloss Multitask" tape, and it seems to work for me.  Just about anything that's from 3M and is clear will probably work.

Did you make sure that the surfaces you were taping to were clean?  This stuff isn't going to stick well to an oil-soaked surface.

[RandySmith]

Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!

Many of you in this forum know very well Sergey, and you know that he ain't no rookie!

Please, check out the pics attached (and enlight me!)

Thanks!

YES  we are sure  !!!!  

Use thin sealing tape, or packaging tape, you can buy this tape that is thin or thick, the thin tape is easy to find.
It makes the stuntships  turn , stable and consistent. This is the biggest problem when conditions  change, The turn rate will change with light of heavy winds, and slower or faster speeds some times, or most times.
The KEY word here is  "consistent" ie mainly the same in all conditions, plane turn feels the same in winds, and the trim stays .

Randy

[Bob Whitely]

The best tape we have found is called "Moores' Crystal Clear."  It is a mylar
type and goes on smooth and comes off clean when you need to replace it.
Sealing the hingelines is just as important as putting a bellcrank in to move
the surfaces. If you don't tape it up it is not worth flying. It will never fly as
well as it could and is impossible to trim out.  RJ

[Chris Wilson]

Look up 'slotted flaps' on full size aircraft, the slot is designed to accelerate air over the flaps leading edge and thus it sticks better to its surface.

[Doug Moon]

I have used Moores in the past.  Good stuff.  I tried it on my last two planes with no noticeable difference.  So when it wore and needed to come off I didn’t replace it.

I have had planes in the past where sealed lines made a huge difference right off the bat!  It is something to try and trim with on every model.

Let me see if I can get this out of my head and onto the screen correctly.

When you try to make the gap as tight as possible there will still be a small gap there bigger than an air molecule.  When the flap is deflected there is a pressure along that side of the wing and flap.  The air will find the open spot in gap and break through causing a small "spout" of air going through the gap to the back side of the deflected surface.  This in turn snaps the air off the back of the flap or disrupts it.  In some cases it isn’t noticeable.  In others the plane won’t be consistent and you can’t trim it out and you go crazy trying.  Seal the lines and BOOM all is well as the air stays on the sides it is supposed to stay on during deflection.

Now the larger gapped on purpose surfaces is doing something different all together.  When this is deflected the air flows through the gap on purpose and over the back of the flap and the front of the flap at the same time.  It is almost as if the surface is receiving its own airflow top and bottom separate from the wing.  Talking with Frank Williams at the Nats he said his "Slot Machine" using slotted flaps similar to what you see here was a beast over head and in the hourglass.  Smooth tension and characteristics like nothing he had ever tried before.  Certainly something to revisit!

[Brad Smith]

When you tape a hinge line do you tape both sides or just one, do you tape just the flaps or the elevator too?

[Brett Buck]

Hello guys,
We ALL know -and this have been proven and sufficiently demostrated through the years- that properly sealed hinge lines is a must in order to get the most out of our planes in terms of flying performance.
Again, I'm sure that EVERYONE agrees with this fact.
Now, can anyone please explain me HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!

Many of you in this forum know very well Sergey, and you know that he ain't no rookie!

   Of course sealing the hinge lines is not mandatory to make the airplane fly. If you very carefully control the way the gaps change as the surfaces move, any ill trim effects will be minimized, and then you adjust around whatever non-linear effects you get from having flow through the gap. People flew that way for decades.

 People also had mysterious and unresolvable trim issues that varied wildly from day to day and from airplane to airplane for decades, too. Usually, through dint of perseverance, lots of trim adjustments and lots of flights to "get used" to the airplane, they came to grips with it. As far as I can see, there isn't a lot of value in doing it that way if there is an alternative.

    Brett

[Jim Hoffman]

When you tape a hinge line do you tape both sides or just one, do you tape just the flaps or the elevator too?

Sealing one side is all that is necessary – most seal the bottom for cosmetic reasons.  Seal flaps and elevator.

Something not stated is that sealing the hinge lines eliminates potential asymmetry due to variation in the gaps.

Jim Hoffman

[Chris McMillin]

If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.   
Chris...

[frank williams]

This was done in my garage wind tunnel back in the late 80's.  The section was a 3" stab and 3" elevator run at ~50mph.  The blue line is with a gap that was "Concours quality", barely the width of a sheet of paper.  The redline was with tape sealing the joint.  Past about 15 deg of elevator deflection, the difference is very significant.

It looks to me like Belko is after an effect of "bumping" the leading edge of the elevator up above the nominal position to help promote an attachment of flow over the top of the surface.

[Chris Wilson]

This was done in my garage wind tunnel back in the late 80's.  The section was a 3" stab and 3" elevator run at ~50mph.  The blue line is with a gap that was "Concours quality", barely the width of a sheet of paper.  The redline was with tape sealing the joint.  Past about 15 deg of elevator deflection, the difference is very significant.

It looks to me like Belko is after an effect of "bumping" the leading edge of the elevator up above the nominal position to help promote an attachment of flow over the top of the surface.

Forgive my naivety here Frank, but is not the lower 'concourse'  curve on your graph less drastic and more predictable in practice?

[Brett Buck]

If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.   
Chris...

  Although I would not discount Al Rabe's "car hood" airfoil testing with regard to these sorts of airfoils/hinges.

  What concerns me most about the various intentional or inevitable gap deals is the non-linearity of the control response. Getting enough lift is a complete non-issue with any reasonable LE radius and modern powerplant/props, so I think designing it for most consistent and linear response is a lot more important. In full-scale acrobatic airplanes you want it to be non-linear and/or stall abruptly, I think, but we certainly don't want that.

   Brett

 

[Mike Keville]

Yes!  We even do this on Old Timers, using 'over-and-under' cloth (or polyester) hinges placed next to each other, full-span.  Makes a world of difference.

[Avaiojet]

Mike,

Really nice looking Ringmaster, yours?

Increased stab/elevator area?

Charles

[Shultzie]

If you hinge like Keith Trostle you won't have to use unsightly tape. They're sealed already. His 1960's Focke Wulf is a good example.
Looks like the model in the picture was trying an old fashioned way of boost, or just trying to excite flow by sticking the balance into the boundary layer aft of the hingeline. His hinges are around 10 to 20% of the flap chord, little less on the elevator. It works on real acro airplanes to an extent.  
Chris...

[Mike Keville]

Mike,

Really nice looking Ringmaster, yours?

Increased stab/elevator area?

Charles

Yes, mine....from 2005/2006.  Long gone now.  And yes, stock stab/elev area.  Camera angle probably makes it look larger.

[frank williams]

Forgive my naivety here Frank, but is not the lower 'concourse'  curve on your graph less drastic and more predictable in practice?

Chris
Yes it might appear that way because I didn't focus in with alot of measurements around the zero elevator deflection, for either configuration.  I was really looking at the linearity of the curve and the maximum force produced.  So you're correct that maybe this chart isn't totally germaine to the discussion at hand.  I found interesting that there was 20% more force produced by the stab/elev section at an elevator deflection of 25 degrees.

What we really need to see, is how the curves vary with different gap widths, around a zero elevator deflection.  I stopped when I saw that the sealed curve was very linear and had a significant increase in maximum lift.

[Claudio Chacon]

OK Gentlemen! Thank you VERY much for all your enlightening contributions!
Mr. Frank Williams graphic was a real eye opener!

Thanks again,
Claudio.

[Chuck_Smith]

Often, aileron hinge points on full size aircraft are located ahead of the gap.  Aileron deflection causes the leading edge to move in the opposite direction of the main flap area deflection. The resulting "scoop" actually enhances aileron lift.

Floyd

Floyd, that's not quite true. We do that to balance the forces and reduce the moment, this lowering the control forces. Notice that it was prevalent on older aircraft with cable controls, after hydraulic actuators connected to servo valves came alone, the balance area disappears.

The balance area creates a lot of drag (and can lend themselves to flutter problems). Sealed gaps increase efficiency and reduce moments, so it's win-win.

[Ted Fancher]

The real question to be asked is:

What harm can it do if the hinge tape is properly applied?

Ted Fancher

p.s.  The whole stunt world discussion of sealed hinge lines started many years ago after I brought it up in one of my old Model Aviation columns. 

That is "NOT", however, an attempt to take credit for it.  The credit goes to Denny Adamisin who brought up the fact that he routinellysealed his hinge lines during a chance "chow time" get together.  It was more or less like getting slapped in the face!  Why would anyone interested in using lift to make a dog do tricks not do everything possible to maximize and insure the consistency of that prime factor in doing so.  I went home, sealed hinge lines on a couple of semi dogs and never looked back.

The fact that an individual airplane might ultimately prove to have not been noticeably improved does not negate the wisdom of the question above.  The question itself out to be juxtaposed with a second question, by the way.  That would be: "What sort of potential problems can I erase from my trimming list as a result of sealing them as the last step of bench trimming...before the motor is ever started?  The answer to that question would take a lot more words than the answer to the first question.

Why leave a easily closed door open in hopes that it might not freeze tonight?  Shut the dang door,  go to bed and sleep peacefully!

[Tim Wescott]

The real question to be asked is:

What harm can it do if the hinge tape is properly applied?

Well, if your plane is built like Mr. Belko's, then your surfaces won't move any more.

It's certainly an interesting approach, and if I had a lot more time on my hands and flying skills in them, I might even feel motivated to build an airplane or three and see if there was a noticeable difference.  It's definitely not something that lends itself well to an A vs. B comparison.

[Chris Wilson]

Again, look at slotted flaps on full size aircraft.

Its been well proven since the 1920's that properly designed and executed slots between the main wing and the movable control surfaces does increase lift further than attached ones.
(And I quote from a NACA source "While in the case of an ordinary trailing end flap any leakage through a gap between the main wing and the flap seems to be highly detrimental, a combination of a flap and a properly shaped slot proves to be very efficient." NACA Tech report 554 1936.)

The issue is promoting the air acceleration evenly between upright and inverted as most known setups are asymmetrical and complicated to build.

Models will not easily promote that level of complexity thus we 'do what we can when we can' and call it consistency.

All of this seems like a bit of a one sided argument without the author of the model in the original post being present to put his case forward to the jury.

[Bill Little]

Well, this might not be 100% on topic, but I have decided to use "cloth" hinges on all my newly built stunters so as to not have to worry about sealing the hinge lines with tape.

BIG Bear
RNMM/AMM

[Chris Wilson]

The real question to be asked is:

What harm can it do if the hinge tape is properly applied?

Well I would have to disagree somewhat Ted.

I consider it to be "HOW IN THE WORLD could Mr. Sergey Belko get away in 14th. place in the last World Championship with such a HUGE gap in his hinge lines???!!!"

The subject is the deliberate use of a pronounced gap, his successful use of it (more than evidenced by the obvious photos and his placement in serious competition) and never is there any mention of sealing it, tape or otherwise.

Clearly some fliers consider there is work to be done in this area, and for that I applaud him (and for his outstanding range of F2B engines that again ..... are different.)

Thanks.

[Howard Rush]

Full-scale airplanes that have surfaces that deflect both ways (elevators, rudders) typically have hinge lines behind the surface and sealed hinge gaps.  Sealing the gap of a surface hinged behind the LE is hard to do with our size planes without too much friction.  So we choose between sealed hinges at the surface LE or unsealed hinges behind the LE.  The latter has two appealing features: less hinge moment and easy surface removal.  It may be worth doing some experiments or looking up old NACA data to see if we can make surfaces with gapped hinge lines get as much lift and as consistent lift as we get just by sealing our simple hinges.  Theoretically, there's extra lift to be had from properly shaped gaps.  Frank Williams and Wes Dick have done some experimenting and may know how.  Sergey and the Yatsenkos know more than most of us, but from what I've seen and flown, they don't have anything significantly better than our crude sealed flaps.  

[Chuck_Smith]

In aircraft design, the rule is that the change in lift coefficient as a function of flap deflection increases 15 percent for a seal gap over an unsealed one. A good reference is Aircraft Design:A Conceptual Approach by Dan Raymer which by the way, is the one book you should own if you are into the engineering aspects of aircraft design.

Mr. Raymer sets out the first chapters showing why and how, and then in the following chapters actually designs a sport aircraft working through the design process. It's the standard text used for aspiring designers.

[Chuck_Smith]

In aircraft design, the rule is that the change in lift coefficient as a function of flap deflection increases 15 percent for a seal gap over an unsealed one. A good reference is Aircraft Design:A Conceptual Approach by Dan Raymer which by the way, is the one book you should own if you are into the engineering aspects of aircraft design.

Mr. Raymer sets out the first chapters showing why and how, and then in the following chapters actually designs a sport aircraft working through the design process. It's the standard text used for aspiring designers. Yes, it's an engineering text and the math may beyond the scope of the casual reader, but he does great job with the qualitative analysis as well.

It's fascinating, and I refer to it constantly.

[Paul Smith]

There is no need to seal the elevator hinge gap.  You don't need all the tailplane lift you can get - only enough to steer the plane.

It might help to seal the wing flap gap so as to create the maximum possible lift. 

In real planes it is seldom if ever necessary to create all the lift you can possibly get.

[Steve Helmick]

I just went down and checked out the Norm Whittle designed and built Eagle I flew most of last season. There are no seals on either flaps or elevators. The wing TE is squared off and the flap LE is triangular, pretty much as normal practise. The hinges are Robart "Hinge Points", and are notched back into the flaps/elevators much like Mr. Belko's. At neutral, the hinge gap is about the same as the thickness of the cardboard of a line clip pack. The outboard flap has a little more clearance. The interesting thing is that as the surfaces articulate, the hinge gap does not change noticeably. I would have thought a radius would be better. The disadvantage, IMO, is that you can't make the surfaces removeable...which I happen to think is very important.

Norm says it's 638 sq. in., and it weighs 67 oz here on the coast (with 1 oz. of added nose weight to comp for the 2 oz of moisture it absorbed), piped .46VF. Flies pretty darned good, IMO, tho I'm not saying it's wonderful or needing some trim changes. The prop change and nose weight (late Sept.) were big improvements.  I'd like to get PW or Howard to fly it, sometime, but their ears are very sensitive now, ya know.    Steve

[Randy Cuberly]

Full-scale airplanes that have surfaces that deflect both ways (elevators, rudders) typically have hinge lines behind the surface and sealed hinge gaps.  Sealing the gap of a surface hinged behind the LE is hard to do with our size planes without too much friction.  So we choose between sealed hinges at the surface LE or unsealed hinges behind the LE.  The latter has two appealing features: less hinge moment and easy surface removal.  It may be worth doing some experiments or looking up old NACA data to see if we can make surfaces with gapped hinge lines get as much lift and as consistent lift as we get just by sealing our simple hinges.  Theoretically, there's extra lift to be had from properly shaped gaps.  Frank Williams and Wes Dick have done some experimenting and may know how.  Sergey and the Yatsenkos know more than most of us, but from what I've seen and flown, they don't have anything significantly better than our crude sealed flaps.  

Just an observation, but when Sergey came to Tucson a few years ago to fly in a contest here, He took a neat little box out of his rented car, began removing airplane parts from the box, assembled his airplane, to include installing the flaps and elevators onto the flying surfaces, aligned everything and flew the thing without needing to actually trim anything.
The flaps and elevators had fairly large gaps (maybe 3/32 inch) and were hinged behind the flap and elevator leading edges.  I was curious about it but really couldn't quite understand his complete answer, but the best I understood the situation was that the gaps made the flaps less efficient but they were still adequate and because they (the gaps) were fairly large they were easy to make consistent.  With a take apart that has removable flaps etc it would be a lot of trouble to seal the flaps and elevators each time the airplane is taken apart and reassembled.
The airplane had one of his 75's in it and it flew very well.  He won the contest and here in Tucson that's not cherry picking.

Personally I always seal flaps and elevator hinge lines because I had serious trim problems with unsealed hinge lines a long, long time ago, and being primarily a combat flier then, my Stunt Guru at that time (Mr Hoffman) said to always seal them and it works.  However I've never built
wide hinge lines and tried to make them consistent because I always seal them.

Randy Cuberly

[Howard Rush]

No point in having gaps unless: a) you do some science to make sure they're blowing the flaps right, or 2) you hinge the flap aft of the LE, or iii) both.  You can remove the wing and flap together if you use a slot for the control horn to slide into.  The slot only needs to bear a load at its end, when it's in the flying configuration.

[Brett Buck]

There is no need to seal the elevator hinge gap.  You don't need all the tailplane lift you can get - only enough to steer the plane.

It might help to seal the wing flap gap so as to create the maximum possible lift. 

 But, again - getting more lift is not a critical issue. We have had enough lift (in the wing) to do as hard a corner as we want since about 1988.

    The important part about sealing the hinge lines has only peripherally to do with enhancing the lift. A far more important effect is that it tends to remove variability in the lift over the range of control motion. The result is that the airplane is far more consistent in trim, many of the previous problems that people had with "inside/outside" turn differences go away or are significantly reduced, and that the airplane is far more honest over time and over other variations.

     Brett

[Chris Wilson]

So Belko's model has inconsistent trim?

[Brett Buck]

So Belko's model has inconsistent trim?

   I have no idea. Please read above.

   Brett

[Chris Wilson]

   I have no idea. Please read above.

   Brett

Mate, I have no idea also.

The more I read here the less I know.

[Howard Rush]

I presume Brett's observation pertains to the flap configuration we use: hinged at the flap LE with only a small gap betwixt flap and wing.  

[Howard Rush]

Here's a very objective account of Sergei's appearance at the Meet & Meat a few years ago.  Brett made him some parts to fix his plane.  http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=316105&mesg_id=316105&listing_type=search

[Dennis Adamisin]

Hi Claudio
Since I started using sealed hinge gaps I cannot think of a reason to stop - no scenario where the seal might be CAUSING a problem.  I am also pretty sure that sealing the gaps preempt those gaps from causing problems on their own.

I am also very impressed by the plot Frank Williams posted a few posts ago - it provides a solid justification for using seals.

So to answer your question YES I am sure and I always (since 1980) use them.

[Howard Rush]

Does anybody here read what anybody else writes?

[ash]

No.

I mean, yes.

[Keith Renecle]

Are the Yatsenko models like the Shark equipped with sealed hinge lines? I can't remember checking this myself. Maybe Orestes seals his models so someone in the USA will know for sure. I do know however, that they do pretty well all over the globe in competitions. I enjoyed watching Sergei's huge model in Bulgaria. It was an impressive sight and also sounds wonderful. It could be that in the windy and gusty conditions that such a big model is difficult to fly. Either way, Sergei is a very good pilot and such a nice guy as well. Besides Igor's electric Max Bee, I watched Sergei's model the most.

Keith R